My 408 sq ft enclosed patio has a flat concrete roof/deck that water ponds up on and has at least 2 large cracks, which leak into the patio below. The roof/deck appears to be a solid concrete slab, no attic with some kind of coating over it.

The soffits are cracked and there is exposed & rusted re-bar showing.

The roof/deck also has a wooden railing system, which is failing & needs to be removed/replaced BUT it is attached directly right into the roof/deck.

I agree with Oldog, remove all the railling and after repairs are done to concrete intall vinyl decking membrane and go with aluminium railing, if posible go with the one that bolt to the face of the deck so you have no holes in the deck top. The only catch is, it would want to run 6" up behind the siding and under the door threshold.

I'm in the process of removing the railing to replace with aluminum as ideally I'd like to use this deck often and set out patio chairs, etc... I've been assured by a local Structure & Foundation professional whose opinion I have trust in that this is primarily a water issue starting at the main roof down through the soffits, stucco & paint and broken gutters etc..

If it's not too much trouble, I'd appreciate opinions on:
1) "BUR" vs "Waterproofing system".
2) The different "Waterproofing systems".
3) Whether or not it appears necessary to address the cracks on the roof-deck floor before applying new roofing system?

I would repair the surface with some concrete patch and cover the whole thing with vinyl decking and make sure it's water proof, that would invulve cutting the siding back to allow it to run up the wall 6". You should repost the photo of the rebar showing in the concrete forum, someone like Bridgeman would have better suggestion on how to fix that and it dose need to be fixed.